An air mat in which compressed air is introduced into an airtight bag has been already put to practical use. However, an air mat, the whole surface of which is always stretched by air pressure, hinders the blood circulation of the human body surface when used. This disadvantage is not limited to such an air mat but also an air mat formed of urethane foam has the same disadvantage. Therefore, patients who cannot move on the bed, e.g., those in serious illness or affected by an atrophy of muscles, have bedsores and suffer from the weakening of internal organs, especially digestive organs like intestines.
In order to prevent bedsores, air mats have been developed in which a number of slender air bags are provided in a grid-like arrangement, and they are inflated and deflated by controlling the air supply thereinto. (Japanese Utility Model Provisional Publication Nos. 5609/76, 164393/77, 69194/78, 98793/78, and 95596/78).
In order to obtain a sufficient massaging effect by means of such air mats, patients have to lie down directly on the air mat. However, if the patient lies down directly on the air mat, a sufficient ventilation cannot be achieved between the air mat and the body surface of a patient. As the result, disadvantageously, the body surface of the patient becomes wet with prespiration after a long use of the air mat.
An apparatus has been developed in which small holes are provided in the air mat so that air for inflating the air mat can be discharged out through the holes and thereby a compulsory ventilation can be achieved between the air mat and the body surface of the patient (Japanese Utility Model Provisional Publication No. 56096/76). However, with this structure, compressed air fed by a compressor is excessively discharged out of the portion of the mat where the body weight of the patient is not applied. Thus, air is wasted without being used for the ventilation between the human body and the mat. Further disadvantageously with this structure, the body of the patient is put into contact with cold air and is apt to be chilled in winter.